Spermatogenesis is a complex process where the proliferation/differentiation of germ cells is intimately tied to their apoptosis. How these germ cell corpses are cleared and how this engulfment process links to normal spermatogenesis, are poorly understood. Studies in other tissues have shown that corpse clearance is fundamentally important for normal development, and that failed clearance can lead to secondary necrosis of the apoptotic cells and tissue damage. Sertoli cells of testes are important in the engulfment of dying or dead germ cells. However, little is known about the molecules and mechanisms that govern Sertoli cell-mediated engulfment of apoptotic germ cells. Our overall hypothesis is that a set of molecules in Sertoli cells regulates the engulfment of apoptotic germ cells, and that disruption of this engulfment pathway will result in disruption of normal germ cell development in the testes. Here, we will rigorously address the biochemical and biological features of Sertoli cell-mediated germ cell engulfment in vitro and in vivo. We will pursue these studies with the combined expertise of the two PIs on this project, Jeff Lysiak with respect to spermatogenesis and germ cell apoptosis, and Kodi Ravichandran on apoptotic cell recognition and engulfment. We will test the biology of corpse clearance in the testes through the following specific aims. Our preliminary studies suggest the expression in Sertoli cells and a possible role in engulfment for the evolutionarily conserved signaling module composed of ELMO1, Dock180 and Rac proteins. In Aim 1 of this proposal we will use a combination of biochemical, functional and gene silencing studies to rigorously test the hypothesis that this signaling module is involved in Sertoli cell-mediated engulfment of apoptotic germ cells. In Aim 2, through Sertoli cell-specific deletion of engulfment genes using conditional knockout mice, we will attempt to disrupt germ cell corpse clearance in vivo. We will then address the importance of corpse clearance at different levels, including developmental apoptosis in the postnatal testis, injury models, and during spermatogenesis. Taken together, the combination of in vitro, in vivo, and whole animal studies tested here will provide key insights into mechanisms governing germ cell corpse clearance and yield a better understanding of this fundamentally important process for spermatogenesis.